1. Field of the Invention
The present invention relates, in general, to a control system of refrigerator. More particularly, the invention provides a defrost control system for a refrigerator utilizing a cold-accumulation material.
2. Description of the Prior art
It is known to provide a cold-accumulation material in a refrigerating device, such as a refrigerator and an air conditioner to improve the operating efficiency of its refrigerating cycle. An example of such a refrigerating device is disclosed in Japanese Utility Model Publication No. 53-10586, filed on Oct. 9, 1973 in the name of Kenichi KAGAWA. In Japanese Utility Model Publication No. 53-10586, the refrigerating cycle has an auxiliary cooler and an auxiliary condenser located in a case containing the cold-accumulation material. The auxiliary cooler and the auxiliary condenser are connected in parallel fluid circuit with each other. When a load to be cooled by the refrigerator is small, the auxiliary cooler cools the cold-accumulation material thereby accumulating "extra" cooling capacity of the refrigerating cycle in the cold-accumulation material. When the load to be cooled is large the auxiliary condenser compensates for an insufficient condensing capacity of a main condenser exchanging heat with the cold-accumulation material. Thereby, the efficiency of the refrigerating cycle, especially the operating efficiency of its compressor, is improved.
Recently, cold-accumulation materials have been placed in refrigerators for the purpose of evening out power demand during a 24-hour day by utilizing power which would otherwise not be efficiently used, such as, for example, night-time power. Such a refrigerators is, for example, constituted as follows.
A refrigerating cycle is established including a main evaporator for cooling a refrigerator compartment and a cold-accumulation evaporator for cooling the cold-accumulation material. Refrigerant is selectively supplied to the main evaporator and the cold-accumulation evaporator. A cold-air circulation fan is provided in association with the main evaporator to supply and circulate cold air produced by the main evaporator in the interior of the compartment. The cold-accumulation material is installed in such a manner that it can be cooled by the cold-accumulation evaporator. A thermosiphon is provided in fluid circuit with the cold-accumulation material and the main evaporator. The thermosiphon comprises a closed-loop pipeline in which a working fluid circulates. This working fluid cools the main evaporator by transferring heat from the main evaporator to the cold-accumulation material. When there is little power demand, for example, in the middle of night, a compressor in the refrigerating cycle is actuated to supply refrigerant to the cold-accumulation evaporator thereby cooling the cold-accumulation material. For a set time band in the daytime when there is large demand for power, the compressor is not operated and the thermosiphon is made functional. The main evaporator is cooled by exchanging heat between the cold-accumulation material and this main evaporator through the thermosiphon while at the same time the interior of the compartment is cooled by the fan circulating the cold air produced thereby in the interior of the compartment.
A conventional refrigerator is provided with a defrosting device to remove frost accumulated on an evaporator periodically for ensuring optimum cooling efficiency. This defrosting device keeps track of the operation time of the compressor, and actuates a defrost heater when it has operated for a predetermined period of time, usually indicated by a count of a counter. In a conventional refrigerator, generally the amount of frost accumulated on the evaporator is proportional to the time during which air in the compartment flows past the evaporator. There is a definite relationship between the amount of frost accumulated and the compressor's cumulative operation time, since it hss been the practice to operate the compressor and the cold-air circulation fan simultaneously.
However, in a cold-accumulation type refrigerator such as described above, the relationship between the amount of frost and the compressor's cumulative operation time is not the same as for a refrigerator without a cold-accumulation material. Adhesion of frost to the evaporator occurs even when the refrigerator compartments are being cooled by the cold accumulation material by using the thermosiphon and the cold-air circulation fan.
Therefore, it is not appropriate or efficient to utilize the defrost cycle employed in a conventional refrigerator for a coldaccumulation type refrigerator.